IEEE802.11ac is a wireless local area network (LAN) standard and defines a downlink multi-user multiple input multiple output (DL-MU-MIMO) transmission scheme. DL-MU-MIMO uses a technique called “beamforming” and carries out spatially multiplexed transmission by forming spatially orthogonal beams for multiple terminals. The individual terminals eligible for DL-MU-MIMO may be called “users.” As the method for an access point to select multiple terminals to carry out DL-MU-MIMO transmission, there is a method according to which a combination of terminals having a small spatial correlation (inter-user interference) is selected. Also, according to an existing method, a combination of terminals having small difference in frame length of the frames to be transmitted is selected considering the spatial multiplexing efficiency.
The frame lengths of the terminals can be calculated based on the size of the frame and the transmission rate (MCS: Modulation and Coding Scheme) used in transmission of the frames. The MCSs necessary for transmission to the terminals are in normal cases selected based on the SINRs of the respective terminals (Signal-to-Interference Noise Ratio).
However, the inter-user interference amounts of respective combinations of terminals in MU-MIMO differs from each other, so that it is necessary to calculate the inter-user interference amounts (SINR) for each candidate of combination in order to select the MCSs for transmission. In the calculation of the SINR, in normal cases, matrix operation is carried out using a channel matrix. As the number of the combination candidates becomes larger, the calculation amount of the matrix operation also becomes larger, causing increase in the calculation amount of the user selection scheduling.